Ultrawideband electronically scanned arrays (UWB-ESAs) with polarization agility and wide-scan performance remain as a key component in programmable and multifunctional RF front-end systems. Additionally, UWB-ESAs are desirable for use in high-throughput wireless communication systems, high-resolution radar applications, electronic countermeasures, and radio astronomy. However, conventional UWB-ESA technologies are expensive and challenging to fabricate, assemble, and maintain due to non-planar geometries that require vertical integration and the use of external feeding parts such as feed organizers and baluns or hybrid circuits, for example.
Planar UWB-ESA technologies are appealing due to their simplicity, low-cost fabrication, ease of integration, and low-profile. U.S. Pat. No. 6,512,487, for example, discloses a sheet antenna (CSA) array that was among the first planar UWB-ESAs capable of achieving up to 9:1 (high-to-low frequency ratio) bandwidths in a dual-polarized arrangement by using a coincident phase center fed capacitively coupled horizontal dipoles above a ground plane. Other planar arrays such as the fragmented aperture array (FAA; an example of which is disclosed in U.S. Pat. No. 6,323,809), long slot arrays, and thumbtack arrays use connected electric or “magnetic” elements that, when radiating in free space and infinite array configurations, yield infinite bandwidth. To produce unidirectional radiation, a ground plane is introduced that inevitably engenders resonances, and thus lossy screens or frequency selective surfaces, and R-card are introduced between the array and the ground plane to suppress them at the expense of some gain loss, efficiency reduction, and increases in antenna temperature.
Despite exhibiting some satisfactory UWB radiation properties, these conventional UWB-ESAs can be costly, and impossible to manufacture for operation at millimeter-wave (mm-wave) frequencies. ESAs typically include very large, dense two-dimensional grids of periodically-spaced radiators (e.g., 100-70,000 elements). Such large grids of, often complex, radiator elements are impossible to fabricate in one piece. Consequently, assembly from individual elements by pick-and-place is time-consuming or often inhibited due to electrical connection requirements between elements. Accordingly, a modular tile-based design that allows integration of a moderate number of elements in one tile followed by the modular assembly of such tiles would be preferable. In addition, all conventional UWB-ESAs rely on multiple manufacturing technologies (hybrid manufacturing) at different build stages, for example, planar fabrication combined with CNC or EDM machining or 3D printing. These technologies have different tolerances and part size limitations that ultimately prohibit UWB-ESA scalability to higher frequencies, including newly released spectrum bands at EHF mm-waves (30-300 GHz). Related to cost, frequency scalability and electrical performance is the reliance of all conventional UWB-ESAs upon external circuitry such as feed-organizers, wideband passive or active baluns, and/or wideband hybrids. All of these are difficult to integrate to the ESA aperture, can be large and bulky or lossy, and increase cost and weight/profile, while compromising electrical performance.
To circumvent these difficulties, the Planar Ultrawideband Modular Antenna (PUMA) array was developed in 2008 to provide a fully planar, modular UWB array technology, as disclosed in U.S. Pat. No. 8,325,093, for example. Unlike other dual-polarized UWB-ESAs, the PUMA array is fully manufactured with planar etched circuits and plated vias without the use of external baluns/hybrids and feed organizers to allow for a simple, low-cost multilayer PCB fabrication process. The dipole array layer is comprised of planar, horizontal metallic traces fed by non-blind plated vias, where one pin connects a segment to the ground plane and the other connects an adjacent segment to the active fed wire. This simplified construction is based on an unbalanced feed-line scheme that uses an additional plated via to connect the fed horizontal trace to the ground plane, effectively enabling direct connection to standard RF interfaces by mitigating common-modes that would otherwise develop within the operating band at broadside scanning conditions. This feeding additionally allows for modular, tile-based assembly due to the dual-offset egg-crate lattice arrangement and lack of external circuitry. Some examples of such an array demonstrated low VSWR and good scan performance out to 45 degrees over a 3:1 instantaneous bandwidth up to 21 GHz.
Despite exhibiting strong performance with a simple design, the bandwidth of the type of UWB-ESA disclosed in U.S. Pat. No. 8,325,093, for example, was limited to 3:1. This limit is inherently imposed by loop modes spurring from the introduction of the additional plated via on each fed dipole arm. To overcome this, a planar matching network was printed on the opposite side of the ground plane, which effectively boosted the instantaneous bandwidth up to 5:1 in simulations, as described in S. S. Holland and M. N. Vouvakis, “The Planar Ultrawideband Modular Antenna (PUMA) Array,” IEEE Trans. Antennas Propag., vol. 60, pp. 130-140, January 2012. Although the bandwidth was improved to approximately 5:1, such matching network usage restricted the operation to frequencies up to approximately 5 GHz.
Thus, although certain PUMA arrays may provide a low-cost, modular UWB-ESA solution as compared to conventional UWB-ESAs, these PUMA arrays exhibit comparatively low instantaneous bandwidth despite their convenient fabrication and assembly benefits.